The present invention relates to apparatus to control the air-fuel mixture supplied internal combustion engines through a closed loop in accordance with a detected exhaust composition, and in particular to such apparatus provided with means for minimizing control oscillation resulting from external disturbances caused by acceleration or deceleration of the engine.
It is known that the ratio of air-to-fuel of mixture supplied to internal combustion engines can be controlled at a reference point to reduce the noxious exhaust components using a sensed exhaust composition as a control signal to proportion the mass ratio of the mixture. Such a control system constitutes a closed loop including a sensor for detecting the exhaust composition and an integral controller receptive of the control signal to generate a correction signal for the air-fuel mixing and proportioning device such as carburetor or fuel injection system. Because of the inherent transport delay time which is defined as the time required for the air-fuel mixture to reach the cylinders of the engine, be combusted and exhausted and then travel through the exhaust system to the sensor, the integral controller keeps influencing the mixing and proportioning device after the reference point has been passed. As a result the system tends to oscillate even during cruising operation. Since the air-fuel mixture is also related to the throttle position, the exhaust sensor is affected by the change in throttle position such that it provides, during acceleration (or deceleration) an output which differs from those obtained during cruising or constantspeed operation. As a result, the integration prolongs to generate a correction signal of such an amplitude that it takes longer to return to the reference point when the engine enters the cruising state. This time lag during the transient period of engine operations will result in a large amplitude control swing above and below the reference point and could lead to a loss of control.